Methods for Marking Surfaces Using Unmanned Aerial Vehicles

ABSTRACT

Methods and apparatus for UAV-enabled marking of surfaces during manufacture, inspection, or repair of limited-access structures and objects. A UAV is equipped with a marking module that is configured to apply marking patterns (e.g., alignment features) of known dimensions to surfaces. The marking module may include a 2-D plotter that enables free-form drawing capability. The marking process may involve depositing material on the surface. The marking material may be either permanent or removable. A “clean-up” module may be attached to the UAV platform instead of the marking module, and may include solvents and oscillating or vibrating pads to remove the marks via scrubbing. The clean-up module can also be used for initial surface preparation.

BACKGROUND

The present disclosure relates generally to marking systems and, moreparticularly, to methods and systems for marking surfaces of largestructures and objects which are difficult for personnel to access(hereinafter “limited-access structures and objects”).

During manufacturing, inspection, or repair of a limited-accessstructure or object, the process may include marking the surface of thestructure or object. For example, some processes require markings toprovide relative location information for manufacturing, inspection, andrepair applications. Without accurate reference information, thoseapplications may not be able to operate as effectively.

The primary way that visible indicator marks are applied to a surface ofa structure or object by a worker is by manual application, which mayrequire a ladder, scaffolding, or scissor lifts. This can be dangerousand time consuming. In some remote situations, these solutions may notbe available. Ground-based robotic vehicles capable of marking do exist,but ground-based robotic vehicles have limitations in the types ofenvironments that they can service. Unmanned aerial vehicles (UAVs) havea much larger range and require less support equipment to operate thanground-based robotic marking systems. It would be desirable to provide amethod for marking the surface of a limited-access structure or objectusing a UAV during manufacturing, inspection, or repair operations.

SUMMARY

The subject matter disclosed in some detail below is directed to methodsand apparatus for UAV-enabled marking of surfaces during manufacture,inspection, or repair of limited-access structures and objects. Inaccordance with some embodiments, a UAV is equipped with a markingmodule that may be configured to apply marking patterns of knowndimensions to surfaces of a structure or an object. For example, themarking patterns may include alignment features (e.g., a grid) for usein inspection, repair, or manufacturing processes. The modular markingunit proposed herein may be coupled to existing commercial-off-the-shelfUAVs. In accordance with some embodiments, the marking module includes atwo-dimensional plotter device (hereinafter “2-D plotter”) that enablesfree-form drawing capability.

More specifically, the marking module includes a module frame that iscoupled (rotatably and/or releasably) to a body frame of the UAV. Themarking module further includes at least one marking device supported bythe module frame. In accordance with some embodiments, the markingmodule may be carried by the UAV to the target object, attached to thesurface of the target object, and then uncoupled from the UAV, allowingthe UAV to fly other missions while the marking module performs amarking task. In accordance with other embodiments, the module frame ispivotably coupled to the body frame of the UAV, which enables the moduleframe to adjust to different surface orientations as the marking moduleis placed in contact with a surface. In this case, the module frame isequipped with a plurality of compliant stabilizers which maintain themarking device in a suitable location relative to the surface to bemarked.

In accordance with various embodiments, the marking process may involvedepositing material on a surface or laser scoring the surface. Forexample, the marks may be made by depositing a visible material, such asink, dye, or paint, using a pen-based element such as a permanentmarker, a dry or a wet erase marker, or ink jet marking. The markingmodule may include a vibration actuator that is coupled to the markingdevice to enable consistent marking of the surface. In one proposedimplementation, the visible material may also be detectable using anultrasonic transducer array or an eddy current sensor. In accordancewith other embodiments, permanent marks may be made by etching (e.g.,using a laser).

The marking material may be either permanent or removable. In the lattercase, a mark removal process is also described below. For cases in whichthe marks are removable, a “clean-up” module may be attached to the UAVplatform instead of the marking module, and may include solvents andoscillating or vibrating pads to remove the marks via scrubbing whenthey are no longer needed. The clean-up module can also be used forinitial surface preparation.

Although various embodiments of methods and apparatus for UAV-enabledmarking of surfaces of limited-access structures and objects aredescribed in some detail later herein, one or more of those embodimentsmay be characterized by one or more of the following aspects.

One aspect of the subject matter disclosed in detail below is anapparatus for marking a surface of a structure or object, the apparatuscomprising: a first frame; a plurality of rotor motors mounted to thefirst frame and capable of producing lift greater than a weight of theapparatus; a plurality of rotors operatively coupled to respective rotormotors of the plurality of rotor motors; a controller programmed tocontrol the rotor motors in a manner that produces lift greater than theweight of the apparatus; a linear actuator coupled to the first frame; asecond frame pivotably coupled to the linear actuator; first and secondcompliant stabilizers supported by the second frame; and a markingdevice supported by the second frame. The first marking device and thefirst and second compliant stabilizers are arranged so that the firstand second compliant stabilizers contact the target surface before thefirst marking device contacts the target surface as the second frameapproaches the target surface.

In accordance with some embodiments of the apparatus described in theimmediately preceding paragraph, the marking device comprises a contacttip that applies ink, dye or paint. Optionally, the apparatus furthercomprises a vibration actuator coupled to the first marking device. Inanother embodiment, the marking device is a laser.

Another aspect of the subject matter disclosed in detail below is anapparatus for marking a surface of a structure or object, the apparatuscomprising: a first frame; a plurality of rotor motors mounted to thefirst frame and capable of producing lift greater than a weight of theapparatus; a plurality of rotors operatively coupled to respective rotormotors of the plurality of rotor motors; a first controller programmedto control the rotor motors in a manner that produces lift greater thanthe weight of the apparatus; an arm rotatably coupled to the first frameand having a distal end; a second frame coupled to the distal end of thearm; a 2-D plotter movably coupled to the second frame; a marking devicesupported by the 2-D plotter; and a second controller programmed tocontrol the plotter so that the marking device follows a pre-definedmotion path. In accordance with some embodiments, the second frame isreleasably coupled to the first frame and the apparatus furthercomprises a plurality of surface attachment devices mounted to thesecond frame.

A further aspect of the subject matter disclosed in detail below is amethod for marking a surface of a structure or object using an unmannedaerial vehicle, the method comprising: (a) coupling a marking module toan unmanned aerial vehicle; (b) flying the unmanned aerial vehicle to alocation in proximity to the surface while carrying the marking module;(c) placing the marking module into contact with the surface; (d)marking the surface using a marking device of the marking module whilethe marking module is in contact with the surface; (e) coupling aclean-up module to an unmanned aerial vehicle; (f) flying the unmannedaerial vehicle to a location in proximity to the surface while carryingthe clean-up module; (g) placing the clean-up module into contact withthe surface; and (h) removing the marking from the surface using acleaning element of the clean-up module while the clean-up module is incontact with the surface. For example, the cleaning element may be ascrubbing pad, cleaning wipe, or liquid spray.

Yet another aspect is a method for marking a surface of a structure orobject using an unmanned aerial vehicle, the method comprising: (a)coupling a marking module to an unmanned aerial vehicle; (b) flying theunmanned aerial vehicle to a position where compliant stabilizers of themarking module contact the surface; (c) while the compliant stabilizersare in contact with the surface, displacing a module frame of the moduletoward the surface until a contact tip of the marking device contactsthe surface; and (d) vibrating the marking device while the contact tipis in contact with the surface.

Other aspects of methods and apparatus for marking of surfaces ofUAV-accessible structures and objects are disclosed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, functions and advantages discussed in the precedingsection may be achieved independently in various embodiments or may becombined in yet other embodiments. Various embodiments will behereinafter described with reference to drawings for the purpose ofillustrating the above-described and other aspects. None of the diagramsbriefly described in this section are drawn to scale.

FIG. 1 is a diagram representing a three-dimensional view of a UAVflying in proximity to a target object in anticipation of executing amarking task.

FIG. 2 is a flowchart identifying steps of a method for UAV-enabledmarking of a surface of a limited-access structure or object inaccordance with one embodiment.

FIG. 3A is a diagram representing a side view of a markingmodule-carrying UAV in accordance with one embodiment in which themarking module is coupled to the ends of two racks of a rack-and-pinionsystem.

FIG. 3B is a diagram representing a bottom view of the UAV depicted inFIG. 3A.

FIGS. 3C and 3D are diagrams representing front views of the UAVdepicted in FIG. 3A. The marking module carried by the UAV is shown intwo states: with a roll angle equal to zero (FIG. 3C) and with anon-zero roll angle (FIG. 3D).

FIGS. 4A and 4B are diagrams representing front views of a module frame14 pivotably coupled to the ends of two racks of a rack-and-pinionsystem in a manner to allow the module frame to rotate about the rollaxis without constraint due to the fixed distance between pivot points.

FIG. 5 is a diagram representing a side view showing the markingmodule-carrying UAV depicted in FIGS. 3A and 3B at two differentinstants in time: as the UAV flies toward (approaches) a surface andwhile the UAV hovers in proximity to the surface after landing themarking module on the surface.

FIGS. 5A-5C are respective diagrams showing the marking module-carryingUAV depicted in FIG. 5 at three stages of a marking process inaccordance with one embodiment.

FIG. 6A is a diagram representing a side view of a flying apparatushaving a marking module carried below the UAV and deployed by downwardmovement.

FIG. 6B is a diagram representing a side view of a flying apparatushaving a marking module carried above the UAV and deployed by upwardmovement.

FIG. 7 is a diagram representing a side view of a markingmodule-carrying UAV in accordance with an alternate configuration inwhich a pair of horizontal extensions support a marking module with anorientation suitable for marking vertical and nearly vertical surfaces.

FIGS. 7A and 7B are diagrams representing top and front viewsrespectively of the UAV depicted in FIG. 7 .

FIG. 8 is a diagram representing a side view showing a clean-upmodule-carrying UAV at two different instants in time: as the UAV fliestoward (approaches) a surface and while the UAV hovers in proximity tothe surface after landing the clean-up module on the surface.

FIG. 9 is a block diagram identifying some components of a system forUAV-enabled marking of a surface in accordance with one embodiment.

FIG. 10 is a diagram representing a side view of a markingmodule-carrying UAV in accordance with another embodiment in which themarking module is coupled to a distal end of a telescoping arm mountedto a rotating ring incorporated in the UAV.

FIGS. 10A-10C are diagrams representing top, side, and front viewsrespectively of the UAV depicted in FIG. 10 .

FIGS. 11A-11D are diagrams representing respective three-dimensionalviews of a UAV having a pivotable arm for carrying a payload atsuccessive stages during a process of transporting and placing thepayload on a surface of a limited-access structure or object.

FIG. 12A is a diagram representing a side view of a marking moduleincluding a marking device having a contact tip in accordance with oneembodiment, which marking module may be a payload carried by a UAV ofthe types depicted in FIG. 10A or a type having a different design.

FIG. 12B is a diagram representing a side view of a marking moduleincluding a laser in accordance with another embodiment, which markingmodule may be a payload carried by a UAV of the type depicted in FIG.12A or a type having a different design.

FIG. 13 is a diagram showing a top view of an electro-mechanical 2-Dplotter overlying a dent or gouge or other cavity-type anomaly wherematerial has been removed from the surface (hereinafter “cavity”). Theplotter includes a holder that holds a marking device, such as themarking device shown in either FIG. 12A or FIG. 12B.

FIG. 14 is a diagram showing a top view of an electro-mechanical 2-Dplotter in accordance with an alternative embodiment. The plotterincludes a carriage that carries a marking device and is translatablealong a traveling bridge having an axis, which traveling bridge in turnis translatable along another axis which is perpendicular to the bridgeaxis.

FIG. 14A is a diagram showing a side view of portions of theelectro-mechanical 2-D plotter depicted in FIG. 14 .

FIG. 15 is a diagram representing a side view of a marking device in aretracted state.

FIG. 16 is a block diagram identifying components of a control systemthat uses rotation encoders to track the relative location (e.g.,relative to an initial position acquired using a local positioningsystem) of a carriage and activate an actuator to move a marking devicefrom a retracted position to an extended position in which a tip of themarking device contacts the surface to be marked.

FIG. 17 is a block diagram identifying some components of a system thatincludes a control station configured to remotely control a markingmodule in accordance with one embodiment in which a marking device iscarried by an electro-mechanical 2-D plotter.

FIG. 18 is a block diagram identifying some components of a remotelycontrolled UAV configured to carry a module.

FIG. 19 is a block diagram identifying some components of a system forholding a marking module in a stable position on a surface of astructure using suction cups.

FIG. 20 is a diagram representing a bottom view of an electro-mechanical2-D plotter (absent the carriage that carries the marking device) inaccordance with an alternative embodiment.

FIG. 21 is a diagram identifying some components of a system forstabilizing a distal end of an extended-reach arm using pneumaticcylinders having rod lock mechanisms.

FIG. 22 is a block diagram identifying some components of a stabilizerfixedly coupled to an end effector, which stabilizer comprisestelescoped tubes, a spring and a contactor.

FIG. 23 is a block diagram identifying components of a control systemthat uses rotation encoders to track the relative location (e.g.,relative to an initial location acquired using a local positioningsystem) of a marking device.

FIG. 24 is a diagram representing a plan view of an anomalous area on asurface having markings arranged to form an alignment pattern overlyingan anomaly for use in an alignment task preliminary to repair of theanomalous area.

Reference will hereinafter be made to the drawings in which similarelements in different drawings bear the same reference numerals.

DETAILED DESCRIPTION

For the purpose of illustration, methods and apparatus for marking ofsurfaces of UAV-accessible structures and objects will now be describedin detail. However, not all features of an actual implementation aredescribed in this specification. A person skilled in the art willappreciate that in the development of any such embodiment, numerousimplementation-specific decisions must be made to achieve thedeveloper's specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

The concepts disclosed herein may be reduced to practice using UAVs of atype that is capable of hovering near a surface to be marked. Inaccordance with the embodiments disclosed in some detail below, the UAVis a rotorcraft having multiple rotors. In some UAVs, each rotor has twomutually diametrically opposed rotor blades. However, in alternativeimplementations, UAVs having rotors with more than two rotor blades maybe used. As used herein, the term “rotor” refers to a rotating devicethat includes a rotor mast, a rotor hub mounted to one end of the rotormast, and two or more rotor blades extending radially outward from therotor hub. In the embodiments disclosed herein, the rotor mast ismechanically coupled to an output shaft of a drive motor, referred tohereinafter as a “rotor motor”. The rotor motor drives rotation of therotor. As used herein, the term “rotor system” means a combination ofcomponents, including at least a plurality of rotors and a controllerconfigured to control rotor rotation rate to generate sufficientaerodynamic lift force to support the weight of the UAV and sufficientthrust to counteract aerodynamic drag in forward flight. The UAVsdisclosed herein further include a controller which preferably takes theform of a plurality of rotor motor controllers that communicate with anon-board computer configured to coordinate the respective rotations ofrotors. The controller is configured (e.g., programmed) to control therotors to cause the UAV to fly along a flight path to a location wherethe UAV (or a module carried by the UAV) is in proximity to or incontact with an area on the surface of a structure to be marked. (Asused herein, the term “location” comprises position in athree-dimensional coordinate system and orientation relative to thatcoordinate system.)

During manufacturing, inspection, or repair of a limited-accessstructure or object, the involved processes may include marking thesurface of the structure or object for various purposes. For example,some processes require markings to provide relative location referenceinformation for manufacturing, inspection, and repair applications. Thisdisclosure describes methods and apparatus involving UAV-enabled markingfor such purposes.

FIG. 1 is a diagram representing a three-dimensional view of a UAV 2flying in proximity to a target object 100 in anticipation of executinga marking task. In the example depicted in FIG. 1 , the target object100 is an aircraft. However, the target object 100 may be a ship, anengine, a satellite, a rocket, etc. In addition, a marker-equipped UAVmay be used to mark structures such as buildings, bridges, towers, andwind turbines. In accordance with the exemplary scenario depicted inFIG. 1 , the UAV 2 may be equipped with a marking module (not shown inFIG. 1 ) for marking an area of interest on the surface of an aircraftwing 110 of the aircraft. The area of interest may be an inspection areathat may include an anomaly 1 (e.g., a dent or gouge). In accordancewith the embodiments disclosed herein, the marking module includes amarking device for marking surfaces of UAV-accessible structures andobjects.

In order to make a viable marking system that uses a UAV as the deliveryplatform, the marking system should be able to address a full range oforientations of the surface (horizontal, vertical, and angled), whilenot destabilizing the flight control of the UAV or interfering with therotors. It should also be able to apply the markings to the surfacewithout jitter. In accordance with the embodiments described below, theUAV 2 seen in FIG. 1 carries an end effector in the form of a markingmodule that includes one or more marking devices. In accordance withsome embodiments, the marking module also includes a plurality ofcompliant stabilizers. In cases where the markings are not permanent,the marking module may be further equipped with devices for cleaning upthe marks after the tasks have been completed.

In accordance with another embodiment of a UAV-enabled marking system,the UAV 2 may be equipped with a selected one of a plurality ofinterchangeable modules, such as a marking module and a clean-up module.In this case, the marking module is coupled to the UAV and then themarking module-equipped UAV flies to the marking site to perform amarking operation. Upon completion of the marking task, the UAV returnsto its original location, where the marking module is removed and theclean-up module is installed. Then the clean-up module-equipped UAVflies to the marking site to perform a marking removal process. In someembodiments the marking module may contain clean-up elements in additionto marking elements, and may include on-board actuators to swap theconfiguration between marking and cleaning.

FIG. 2 is a flowchart identifying steps of a method 200 for UAV-enabledmarking of a surface of a limited-access structure or object inaccordance with one embodiment. The method 200 starts by coupling amarking module to a UAV (step 202) and selecting a marking pattern (step204). For example, the marking module controller may be programmed tocontrol the marking process to achieve the selected pattern. To performthe marking task, the UAV flies to a location in proximity to thesurface to be marked while carrying the marking module (step 206). Thenthe marking module is displaced into contact with the surface (step208). While the marking module is in contact with the surface, thesurface may be marked by computer control of the marking module (step210). Then the UAV flies back to the UAV depot (step 212) and themanufacturing or maintenance task is performed using the marking module(step 214). Meanwhile, at the UAV depot the marking module is removed(step 216) and a clean-up module is installed (step 218). Then the UAVflies back to a location in proximity to the marked surface whilecarrying the clean-up module (step 220) and then displaces the clean-upmodule into contact with the surface (step 222). The markings areremoved from the surface using a cleaning element, such as a scrubbingpad, of the clean-up module while the clean-up module is in contact withthe surface (step 224). After the markings have been removed, the UAVflies back to the UAV depot (226).

Various embodiments of marking modules will be described in some detailbelow. The marking module carried by the UAV 2 seen in FIG. 1 may haveone or more marking devices. In accordance with some embodiments, aplurality of fixed marking devices may be fixedly coupled to the markingmodule to form respective marks (e.g., dots) which are printedconcurrently. In accordance with other embodiments, the marking modulemay be configured to move a single marking device in a manner thatenables free-form line drawing capability. As used herein, the phrase“fixedly coupled to” as applied to two parts means that one of the partsis either affixed to or integrally formed with the other part. As usedherein, the term “affixed” should be construed broadly to encompass allof the following types of fixation: welding, adhesive bonding, andfastening.

FIG. 3A is a diagram representing a side view of a markingmodule-carrying UAV 2 in accordance with one embodiment in which themarking module is pivotably coupled to the ends of two mutually parallelracks 94 (only one of which is visible in FIG. 3A) of a rack-and-pinionarrangement, each of which is coupled to a linear guide (not shown) toconstrain the parallel racks 94 to vertical motion. Only one pivot joint98 a of a pair of pivot joints is visible in FIG. 3A. As seen in FIG.3A, the UAV 2 includes a body frame 4, a plurality of (e.g., four) rotormotors 12 mounted to the body frame 4, and a plurality of (e.g., four)rotors respectively operatively coupled to the plurality of rotor motors12. The body frame 4 includes the central body of the UAV 2 and therotor support arms. Optionally, the UAV 2 may be equipped with one ormore video cameras and lighting elements (neither of which are shown inFIG. 3A) to assist the remote operator to control the system anddetermine where to put the marks.

FIG. 3B is a diagram representing a bottom view of the UAV 2 depicted inFIG. 3A. As seen in FIG. 3B, the marking module 25 includes a moduleframe 14 that supports a plurality of marking devices 24 and a pluralityof compliant stabilizers 48. In the example depicted in FIG. 3B, thereare four marking devices 24 and four compliant stabilizers 48. The fourmarking devices 24 may be positioned at the four vertices of arectangle. During a marking operation, a surface may be marked bypressing the tips of the four marking devices 24 against the surface inunison.

FIG. 3C is a diagram representing a front view of the UAV 2 depicted inFIG. 3A. The marking module 25 carried by the UAV 2 is shown with a rollangle of the marking module equal to zero in FIG. 3C. In contrast, FIG.3D shows the marking module 25 oriented with a non-zero roll angle. Thefreedom to rotate about the roll axis enables the marking module 25 toadjust its orientation so that all compliant stabilizers 48 touch thesurface during landing.

As seen in FIGS. 3C and 3D, the UAV 2 includes a pair of linearactuators in the form of respective rack-and-pinion combinations. Onelinear actuator includes a rack 94 a which is driven to translatevertically relative to a horizontal body frame 4 by rotation of a piniongear 96 a. The other linear actuator includes a rack 94 b which isdriven to translate vertically relative to the body frame 4 by rotationof a pinion gear 96 b. The racks 94 a and 94 b are mutually parallel,but are able to translate vertically independently. Each pinion gear 96a/96 b is coupled to the output shaft of a respective pinion gear motor(not shown in FIGS. 3A-3D, but see pinion gear motors 95 a and 95 b inFIG. 9 ). Each rack 94 a/94 b is vertically translatable betweenretracted and extended positions as the associated pinion gears 96 a and96 b rotate, which translation is facilitated by linear guides (notshown in FIGS. 3C and 3D). The pinion gears 96 a and 96 b arebackdrivable so that the racks 94 a and 94 b are compliant whensubjected to a force that opposes rack extension.

FIG. 3D shows a situation in which the racks 94 a and 94 b have beendisplaced downward different distances, which differential displacementcauses the module frame 14 to rotate about the roll axis. The moduleframe 14 of the marking module 25 is pivotably coupled to the bottomends of racks 94 a and 94 b by means of a pair of pivot joints 98 a and98 b. The pivot joints 98 a and 98 b are “compliant” in the sense thatthey adjust their respective positions relative to racks 94 a and 94 bwhile allowing the module frame 14 to rotate about the roll and pitchaxes.

As best seen in FIG. 3B, the module frame 14 includes a cross beam 19that is coupled to the compliant pivot joints 98 a and 98 b. The moduleframe 14 further includes a first beam 29 a extending in oppositedirections from one end of cross beam 19 and a second beam 29 bextending in opposite directions from the other end of cross beam 19.The marking devices 24 are respectively affixed near the distal ends ofthe beams 29 a and 29 b. In the example configuration depicted in FIG.3B, the marking devices 24 are arranged at the four corners of arectangle. In this configuration, marking devices 24 may be pressedagainst a surface to form four ink spots in a rectangular array on asurface. The compliant stabilizers 48 are respectively affixed to beams29 a and 29 b near the marking devices 24. As seen in FIG. 3A, when therack 94 is retracted, the tips of compliant stabilizers 48 are disposedat an elevation which is lower than the elevation of the tips of themarking devices 24.

FIG. 3A shows the marking module 25 in a retracted position wherein thetips of the compliant stabilizers 48 do not extend below the plane ofthe landing legs 49. FIG. 3C shows the marking module 25 in an extendedposition wherein the tips of the compliant stabilizers 48 extend belowthe plane of the landing legs 49 with a roll angle of the marking moduleequal to zero degrees. This location of the marking module 25 isachieved by displacing the racks 94 a and 94 b downward equal distances.FIG. 3D shows the marking module 25 in an extended position wherein themodule frame 14 is disposed below the plane of landing legs 49 with anon-zero roll angle. This location of the marking module 25 is achievedby further displacing the racks 94 a and 94 b downward by unequaldistances.

The pivot joints 98 a and 98 b may be designed to address two axes ofrotation (roll and pitch) and a small amount of sideways translationduring rotation of the marking module 25. For the two axes of rotation,having joints with axes of rotation at a right angle to each other willaddress the rotation problem. If one of the angles is small, it issometimes possible to handle that with a flexible bushing mount (similarto how a car suspension bushing works). Bushings can also handle a smallamount of translation as well, but if the translation is too great forthe bushing to handle, then a translational element, such as a pin thatcan slide along the axis of rotation of the bushing, may be provided toaddress the change in roll angle of a line intersecting the respectiveroll axes of the pivot joints 98 a and 98 b, which have a fixedseparation distance as the marking module 25 rotates.

FIGS. 4A and 4B are diagrams representing front views of a module frame14 pivotably coupled by means of pivot joints 98 a and 98 b to the endsof racks 94 a and 94 b in a manner to allow the module frame 14 torotate about the roll axis without constraint due to the fixed distanceseparating pivot joints 98 a and 98 b. The pivot joint 98 a includesbearings 83 a and 85 a which have respective axes of rotation which aremutually orthogonal. Similarly, the pivot joint 98 b includes bearings83 b and 85 b which have respective axes of rotation which are mutuallyorthogonal.

Referring to FIG. 4A, one pin 81 a is affixed to the end of rack 94 a,while another pin 81 b is affixed to the end of rack 94 b. When theracks 94 a and 94 b are at the same elevation as depicted in FIG. 4A,the pins 81 a and 81 b are coaxial and project outwardly in oppositedirections. In addition, one bearing 83 a is slidably coupled to the pin81 a, while another bearing 83 b is slidably coupled to the pin 81 b. Inother words, the pins 81 a and 81 b respectively slide through thecenters of bearing 83 a and 83 b. In the state depicted in FIG. 4A, thebearings 83 a and 83 b are separated from racks 94 a and 94 b byrespective nominal bearing separation distances.

FIG. 4B depicts a state of the UAV 2 after rack 94 a has been displaceddownward relative to rack 94 b. During relative displacement, the moduleframe 14 is rotated to the non-zero roll angle depicted in FIG. 4B. Dueto the slidable coupling of bearings 83 a and 83 b to pins 81 a and 81 brespectively, bearings 83 a and 83 b are able to adjust their respectivepositions relative to racks 94 a and 94 b. In the example depicted inFIG. 4B, the arrows indicate that bearings 83 a and 83 b move towardeach other, i.e., toward respective racks 94 a and 94 b. This positionaladjustability eliminates rotational constraints when the distanceseparating bearings 85 a and 85 b is fixed. In alternative embodiments,the pivot joints 98 a and 98 b may be flexibly coupled to module frame14 using rubber bushings to provide compliance.

FIG. 5 is a diagram representing a side view showing the apparatus attwo different instants in time: (a) as the UAV 2 flies toward(approaches) a surface 9; and (b) when the UAV 2 is positioned to hoverclose enough to surface 9 that the marking operation may be performed.During the approach phase, the racks 94 a and 94 b are in respectivefully retracted positions and the roll angle of module frame 14 equalszero. During the marking operation, the racks 94 a and 94 b are extendedrespective distances to cause module frame 14 to rotate (by contact withthe surface) to an angular position that matches the orientation ofsurface 9. The compliant stabilizers 48 are designed to prevent lateralmotion of the marking module 25 relative to the surface during marking.In accordance with one proposed implementation, each compliantstabilizer 48 may include a foot pad that contacts the surface 9. Thefoot pad may be made of an anti-skid material (such as rubber) or may beconfigured as a suction or electro-adhesion device.

The marking devices 24 may be pen-based elements such as permanentmarkers, dry and wet erase markers, or ink jet nozzles. In one proposedimplementation, the marking devices 24 are pens of a type that applymarking material more efficiently when the pens are vibrated. In thiscase, the vibration actuators (not shown in FIG. 5 , but see vibrationactuators 33 in FIG. 9 ) may be connected to each marking device 24. Thevibration actuators 33 are activated to cause the marking devices 24 tovibrate while in contact with surface 9, which vibration enables moreconsistent markings. For situations where the marks do not need to beremoved, laser-based etching may be used.

In accordance with other embodiments, the marking material is detectableby some types of non-destructive inspection (NDI) scans. Having amarking material that can be detected by both NDI and visual means(photographs) can help with data alignment/correlation between the twotypes of data. For example, metallized inks or paint can be picked up byeddy current scanners, and materials with a different density than thescanned area, such as rubberized or plastic-based paints, can bedetected by ultrasound scanners. Also, it may be useful in somesituations to have more than one type of marker material onboard themarking system. This would allow the system to put down some marks thatthe NDI system can detect and others that are for visualdetection—without having to switch out the material module.

FIGS. 5A-5C are respective diagrams representing a side view showing themarking module-carrying UAV 2 depicted in FIG. 4 at three stages of amarking process in accordance with one embodiment. The upper portion ofFIG. 4 showed the UAV 2 in a state wherein the racks 94 a and 94 b areretracted. FIG. 5A shows the UAV 2 at a hovering position above thesurface 9 as the racks 94 a and 94 b are extended (indicated by thedownward-pointing arrow in FIG. 5A). During rack extension, the moduleframe 14 is lowered toward the surface 9. FIG. 5A shows the module frame14 with the compliant stabilizers 48 fully extended, but not yettouching surface 9, although one of the compliant stabilizers 48 isnearly touching.

As the racks 94 a and 94 b continue to extend, one or two compliantstabilizers 48 come into contact with surface 9 and cease to descend, atwhich stage the pivot joints 98 a and 98 b continue to descend towardthe surface 9. Due to the contact of compliant stabilizers 48 withsurface 9, the module frame 14 rotates about the descending pivot joints98 a and 98 b (as indicated by the curved arrow in FIG. 5B) until thetips of all compliant stabilizers 48 are in contact with surface 9, asdepicted in FIG. 5B. The angle of surface 9 determines the roll angle ofthe module frame 14.

While the tips of all compliant stabilizers 48 are in contact withsurface 9, the racks 94 a and 94 b continue to extend to cause themodule frame 14 to descend. As will be described in more detail laterwith reference to FIG. 22 , each compliant stabilizer 48 may comprise anouter tube 82 that is affixed to the module frame 14, a spring-loadedinner shaft 86 that translates between extended and retracted positions,and a contactor 88 affixed to a distal end of the inner shaft 86. Themodule frame 14 is moved downward with sufficient force to cause thecompliant stabilizers 48 to retract until the contact tips of allmarking devices 24 are in contact with surface 9, as depicted in FIG.5C. At this stage, the vibration actuators (not shown in FIGS. 5A-5C)are activated to assist the marking devices 24 to make consistent markson surface 9.

The technology proposed herein may be used to mark surfaces oflimited-access objects such the aircraft seen in FIG. 1 or surfaces oflimited-access structures such as storage tanks and wind turbines. FIG.6A is a diagram representing a side view of a UAV 2 equipped with amarking module 25 that has been placed on a surface 9 of a target object100. Only an upper portion of target object 100 is shown in FIG. 6A.Because the marking module 25 is disposed below the UAV 2, the UAV 2 mayapproach the surface 9 from above and then lower the marking module 25into contact with the surface 9. The compliant stabilizers 48 are ableto retract to the extent necessary to enable the tips of all markingdevices 24 to contact the curved surface.

In an alternative configuration shown in FIG. 6B, the marking module 25is disposed above rotors 10 of UAV 2, which enables UAV 2 to approachsurface 9 of target object 100 from below and then raise marking module25 into contact with surface 9. Only a lower portion of target object100 is shown in FIG. 6B. Again, the compliant stabilizers 48 are able toretract to the extent necessary to enable the tips of all markingdevices 24 to contact the curved surface.

FIG. 7 is a diagram representing a side view of a markingmodule-carrying UAV 2 in accordance with an alternate configuration formarking vertical and nearly vertical surfaces. Instead of a pair ofpivot joints 98 being coupled to the lower ends of a pair of racks 94which, in turn, are coupled to body frame 4 by linear guides (notshown), the pivot joints 98 a and 98 b (only pivot joint 98 a is visiblein FIG. 7 ) are coupled to distal ends of a pair of horizontal extensionarms 61 a and 61 b (only horizontal extension arm 61 a is visible inFIG. 7 ; horizontal extension arm 61 b is visible in FIG. 7A.) Themarking module 25 is thus pivotably coupled to the ends of thehorizontal extension arms 61 a and 61 b.

In the scenario depicted in FIG. 7 , the UAV 2 may fly laterally fromleft to right until the marking module 25 lands on the surface 9 of astorage tank 12 (or other structure or object having a vertical ornearly vertical surface to be marked). The horizontal extension arms 61a and 61 b have a length sufficient to ensure that the marking module 25lands on the surface 9—thereby halting further lateral movement of theUAV 2—before rotors 10 have a chance to strike the surface 9.Intermediate portions of horizontal extension arms 61 a and 61 b areaffixed to the upper ends of the racks 94. Thus, the horizontalextension arms 61 a and 61 b and rack 94 translate vertically in tandem.A counterweight 39 is attached to the other ends of horizontal extensionarms 61 to balance the weight of the marking module 25.

FIGS. 7A and 7B are diagrams representing top and front viewsrespectively of the UAV 2 depicted in FIG. 7 . As best seen in FIG. 7A,the module frame 14 is pivotably coupled to the distal ends of a pair ofhorizontal extension arms 61 a and 61 b by means of respective pivotjoints 98 a and 98 b. The subassembly that includes counterweight 39,horizontal extension arms 61 a and 61 b, and marking module 25 isdisplaceable in the vertical direction during level UAV flight by meansof the rack-and-pinion combinations seen in FIG. 7B. The racks 94 a and94 b shown in FIG. 7B are attached to slidable linear guide halves ofthe linear guides 58 a and 58 b which are partly visible in FIG. 7A.

As previously mentioned, a “clean-up” module may be attached to the UAVplatform instead of the marking module, and may include solvents andoscillating or vibrating pads to remove the marks when they are nolonger needed. The clean-up module can also be used for initial surfacepreparation. FIG. 8 is a diagram representing a side view showing aclean-up module-carrying UAV at two different instants in time: (a) asthe UAV 2 flies toward (approaches) a surface 9; and (b) when the UAV 2is hovering at a location close enough to surface 9 to enable removal ofthe markings by a clean-up module 45.

As seen in FIG. 8 , the UAV 2 includes a body frame 4, a plurality ofrotor motors 12 mounted to body frame 4, and a plurality of rotors 10respectively operatively coupled to rotor motors 12, as previouslydescribed. Optionally, the UAV 2 may be equipped with one or more videocameras and lighting elements (not shown in FIG. 8 ) to assist theremote operator to control the system and determine the location ofmarkings to be removed. In addition, UAV 2 depicted in FIG. 8 includesthe same rack-and-pinion combinations already described in some detailwith reference to FIG. 3C. The UAV 2 depicted in FIG. 8 carries aclean-up module 45 which is pivotably coupled to the ends of a pair ofracks 94 by means of a pair of pivot joints 98 (only one of each pair isvisible in FIG. 8 ). The clean-up module 45 translates verticallyrelative to body frame 4 of UAV 2 in tandem with racks 94.

The clean-up module 45 includes a module frame 14 that is coupled topivot joints 98. In one example embodiment, the module frame 14 supportsa plurality of scrubbing pads 47 and a plurality of compliantstabilizers 48. During the approach phase shown in the upper portion ofFIG. 8 , the racks 94 are retracted and the module frame 14 has a rollangle equal to zero. During the clean-up operation shown in the lowerportion of FIG. 8 , the racks 94 are extended and the module frame 14 isrotated to an angular position that matches the orientation of themarked surface to be cleaned.

Optionally, the clean-up module 45 further includes a respectivevibration actuator (not shown in FIG. 8 ) connected to each scrubbingpad 47 (or other cleaning element) and a subsystem that includes areservoir containing cleaning fluid and a spray nozzle for spraying thatcleaning fluid onto the marked surface. First, the marked surface iswetted with cleaning fluid by spraying and then the vibration actuatorsare activated. The combination of cleaning fluid and vibratory scrubbingaction enables the clean-up module 45 to remove surface marks (anddirt).

FIG. 9 is a block diagram identifying some components of a system forUAV-enabled marking of a surface in accordance with one embodiment. Theflying apparatus depicted in FIG. 9 includes a UAV 2 and a markingmodule 25 carried by UAV 2. The system further includes a controlstation 40 configured to remotely control the flight of UAV 2 and theoperations of pinion gear motors 95 a and 95 b mounted to the body frameof the UAV 2 and the operations of a plurality of vibration actuators 33mounted to the module frame of the marking module 25.

The flight of the UAV 2 is controlled by a flight controller 32 thatincludes a computer 36 and a plurality of motor controllers 35. Thecomputer 36 controls the flight of the UAV 2 by sending commands to themotor controllers 35 which respectively control the operation ofrespective rotor motors 12 that drive rotation of rotors 10. Inaccordance with one flight mode, the computer 36 is configured tocontrol the flight of the UAV 2 as a function of radiofrequency commandstransmitted by a transceiver 44 from a ground-based operations center.Those radiofrequency commands are received by a transceiver 39 on-boardthe UAV 2, converted into the proper digital format, and then forwardedto computer 36 of the flight controller 32. The UAV 2 includes a videocamera 31 (which may be mounted to a pan-tilt mechanism not shown inFIG. 9 ) that provides images for use in flight control or recorded fordocumentation. For example, as the UAV 2 approaches the surface area ofinterest on a limited-access structure or object, the video camera 31may capture images of the area of interest to assist in controlling theUAV 2 so that the marking module 25 can be directed to land on thesurface at a position overlying an area to be marked.

The control station 40 may comprise a general-purpose computer systemconfigured with programming for controlling operations of both the UAV 2and the actuators controlling the marking module 25. For example, thepan and tilt angles of the pan-tilt mechanism, and therefore theorientation of the video camera 31, can be controlled using thekeyboard, mouse, touchpad, or touchscreen of the computer system at thecontrol station 40 or other user interface hardware (e.g., a gamepad).In addition, the computer system of the control station 40 may comprisea display processor configured with software for controlling a displaymonitor (not shown in FIG. 9 ) to display video images of the markedsurface.

As previously described, the UAV 2 includes pinion gears 96 a and 96 bwhich are driven to rotate by pinion gear motors 95 a and 95 brespectively. In accordance with the embodiment represented in FIG. 9 ,the marking module 25 includes a plurality of pens 43. In some types ofpens (e.g., permanent markers), the ink does not flow consistentlyunless there is motion of the marker against the surface. The technologyproposed herein addresses that issue by connecting the pens 43 torespective vibration actuators 33. The control station 40 is configuredto remotely control the operations of pinion gear motors 95 a and 95 band vibration actuators 33.

In accordance with one proposed implementation, the vibration actuators33 are vibration motors of the type that includes miniature eccentricrotating masses. Such vibration motors rely on the rotation of anunbalanced load to create vibration effects. The use of vibration isespecially important on metal or slippery (painted) surfaces. In analternative proposed implementation, means for rotating the pen aboutthe tip are provided. Either the vibration device or the rotating pendevice creates some small amount of motion between the pen and thesurface, which allows the pen to more reliably transfer the ink, insteadof just touching the surface (without vibration) and maybe nottransferring any mark. The use of vibration is optional since it is notneeded for all types of surfaces, but may be useful in marking thosewith lower coefficients of friction.

FIG. 10 is a diagram representing a side view of a markingmodule-carrying UAV 2 in accordance with another embodiment in which themarking module 25 is pivotably coupled to a distal end of a telescopingarm 150, which is in turn connected to a rotating ring mount 114 whichis rotatably coupled to the UAV body frame 4. FIGS. 10A-10C are diagramsrepresenting top, side, and front views respectively of the UAV 2depicted in FIG. 10 . The rotating ring mount 114 includes an inner ring116 mounted to the UAV body frame 4 and an outer ring 118 that isrotatably coupled to the inner ring 116 by means of a multiplicity ofrolling elements 148 (e.g., ball bearings). The rotating ring mount 114enables the telescoping arm 150 to rotate around body frame 4. Thetelescoping arm 150 includes an outer proximal tube 152 affixed to theouter ring 118 and an inner distal tube 151 that is supported by anddisplaceable relative to the outer proximal tube 152. When thetelescoping arm 150 is extended as depicted in FIG. 10 , the markingmodule 25 may be landed on the surface 9. Optionally, the rotatable armsubassembly may include a targeting camera (not shown in FIG. 10 )coupled to outer ring 118. The targeting camera (e.g., a video camera)may be used to capture images of the area on the surface to be marked.

The outer ring 118 is part of a subassembly (hereinafter “rotatable armsubassembly”) that is rotatable about a center of the inner ring 116.The rotatable arm subassembly further includes the telescoping arm 150and a counterweight 135 which are mounted (fixedly coupled) to the outerring 118 at diametrically opposed angular positions. The rotating ringmount 114, telescoping arm 150, and counterweight are designed toprovide a balanced rotational system that allows the telescoping arm 150to rotate about the center of the inner ring 116 without changing thelocation of the center-of-mass of the module-equipped UAV 2. Therotating ring mount 114 enables the pitch angle of the telescoping arm150 to be adjusted as the marking module 25 approaches surface 9. Inaddition, the yaw angle of the telescoping arm 150 may be adjusted bycontrolling the yaw angle of the UAV 2.

The counterweight 135 includes a platform 136 which is attached to orintegrally formed with and extending outward from the outer ring 118.The counterweight 135 further includes arm pitch control motor 132 andan electric power system 134, both of which are mounted to platform 136.The arm pitch control motor 132 drives rotation of the outer ring 118relative to the inner ring 116. The electric power system 134 includes abattery (or battery pack) and associated electronics for providingelectric power to the arm pitch control motor 132 and other electricallypowered components. The counterweight 135 further includes means formechanically coupling the outer ring 118 to the arm pitch control motor132 to enable the latter to drive rotation of outer ring 118 relative toinner ring 116. In accordance with one proposed implementation, themechanical coupling that drives rotation of outer ring 118 includes apinion gear mounted to an output shaft of the arm pitch control motor132 and a ring gear which is mounted to or integrally formed with theouter ring 118 and is engaged by the pinion gear (not shown in FIG. 10). The teeth of the pinion gear are meshed with the teeth of the ringgear, so that outer ring 118 rotates about the UAV pitch axis inresponse to operation of arm pitch control motor 132.

The embodiments described above are designed to mark a surface of alimited-access structure or object at a number of points equal to thenumber of marking devices carried by the UAV. Those marking devices arepre-arranged to produce a desired pattern of dot-shaped marks. Incontrast, various embodiments of apparatus configured to mark thesurface of a limited-access structure or object with free-form linedrawing capability will be described in some detail below. Someembodiments include a mechanical marking device mounted to anelectro-mechanical 2-D plotter. Other embodiments include an opticalmarking device mounted to an electro-mechanical 2-D plotter. Thesemarking modules with plotter form the “payload” that is carried by theUAV. Such a payload may be fixedly or pivotably coupled to the bodyframe of the UAV or may be fixedly coupled to a payload support framewhich is pivotably or releasably coupled to the body frame.

FIGS. 11A through 11D are diagrams representing respectivethree-dimensional views of a UAV 2 having a pivotable arm 3 (hereinafter“arm 3”) for carrying a payload 6 at successive stages during a processof transporting and placing the payload 6 on a surface 9 of a structureor object. The arm 3 is pivotably coupled to the frame 4 of the UAV 2 bymeans of a pivot 5 which is supported by a pivot support 4 a. Thesupport frame 4 a is attached to or integrally formed with frame 4. Thepayload 6 is coupled to one end of arm 3 by a coupling mechanism 15(visible in FIG. 11D). A counterweight 7 is coupled to the other end ofarm 3. The payload 6 and counterweight 7 have respective known weights.Controlling the arm 3 to align the payload 6 with a portion of thesurface 9 involves controlling the arm 3 taking one or more parametersinto account. Specifically, controlling the angular position of arm 3may be based on the arm length, fulcrum point (at pivot 5),counterweight, and payload weight. Controlling the angular position ofarm 3 based on these factors may prevent the UAV 2 from substantiallypitching when aligning the payload 6 with a portion of the surface 9 tobe contacted by the payload 6. The location (position and orientation)of the pivot 5 relative to the surface 9 may be adjusted until thepayload 6 lands on surface 9 by adjusting the location of the UAV 2 asit hovers in the vicinity of surface 9. The angular position of arm 3relative to the body frame 4 of UAV 2 may also be adjusted duringflight.

FIG. 11B depicts the UAV 2 flying toward the surface 9 while the arm 3is oriented generally horizontal. Changing the angle of arm 3 may beaccomplished using a motor (not shown in FIGS. 11A-11D) mounted to thepivot support 4 a and operatively coupled to the arm 3 by a gear trainor a linear actuator (neither of which are shown in FIGS. 11A-11D) thathas one end connected to pivot support 4 a and another end connected toarm 3 at a point located at a distance from pivot 5. FIG. 11C depicts astage wherein the payload 6 is lying flat against the surface 9. FIG.11D depicts a stage wherein the UAV 2 is flying away from the surface 9after the payload 6 has been uncoupled from the arm 3 while in the statedepicted in FIG. 11C. The uncoupled payload 6 may stay attached to thesurface 9 due to attachment forces exerted by a plurality of surfaceattachment devices (not shown in FIGS. 11A-11D), such as magnetic-baseddevices, e.g., an electro-permanent magnet, for ferromagneticstructures, and/or vacuum-based, electrostatic-based, adhesive-based, orgripper-based devices for non-ferromagnetic structure.

In accordance with one embodiment of a method for UAV-enabled marking ofthe surface of a limited-access structure, a marking module-carrying UAVof the type shown in FIG. 3A flies to a location such that the payload 6(e.g., a marking module) overlies to a target area (e.g., a damage area)on the surface of the structure. Then the marking module is activated toapply a pattern of markings (e.g., a grid) while the UAV 2 remainsparked on the surface 9 and holds the marking module in place.

In accordance with an alternative embodiment, the coupling mechanism 15is a quick-disconnect mechanism (e.g., a quick disconnect collet)adapted to hold the payload 6 during flight. The UAV 2 may be flown to alocation in proximity to the target area and then the payload 6 isplaced on the surface 9 of the structure. Surface attachment devicesincorporated in the payload 6 (e.g., a marking module) may then beactivated to temporarily but securely attach the payload 6 to thesurface 9, following which the payload 6 may be uncoupled from the UAV2. The UAV 2 is then free to take off from the surface 9, leaving thepayload 6 (e.g., a marking module) to perform the marking procedure.

The payload-carrying UAV 2 depicted in FIG. 11A is equally well adaptedfor use in marking a wide range of structures including, but not limitedto, aircraft, wind turbine blades, storage tanks, power lines,power-generating facilities, power grids, dams, levees, stadiums, largebuildings, bridges, large antennas and telescopes, water treatmentfacilities, oil refineries, chemical processing plants, high-risebuildings, and infrastructure associated with electric trains andmonorail support structures. The system is also particularly well suitedfor use inside large buildings such as manufacturing facilities andwarehouses. Virtually any structure that would be difficult, costly, ortoo hazardous to be marked manually by a human may potentially be markedusing the systems described herein. The method takes advantage of thebroadening use of UAVs to reduce the cost, time, and ergonomic issuesrelated to manufacturing and maintenance activities in aerospace andother industries.

FIG. 12A is a diagram representing a side view of a marking module 25including a mechanical marking device 24 a in accordance with analternative embodiment, which marking module 25 may be a payload carriedby a UAV 2 of the type depicted in FIG. 11D or a type having a differentdesign. The marking module 25 includes an attachment point 41 which maybe coupled to (and uncoupled from) a distal end of arm 3 of the UAV 2depicted in FIG. 11D. The mechanical marking device 24 a may be amarking tool 11 (e.g., a pen), as depicted in FIG. 12A. In thealternative, the marking device may be electro-mechanical (e.g., an inkjet printer not depicted in FIG. 12A). The marking module 25 incombination with a UAV 2 form an apparatus capable of marking thesurface 9 of a limited-access structure or object.

As seen in the proposed implementation depicted in FIG. 12A, the markingmodule 25 includes a module frame 14 which may consist of rigid orsemi-rigid members which are integrally formed or fastened or joinedtogether. The module frame 14 supports an electro-mechanical 2-D plotter(not shown in FIG. 12A, but see electro-mechanical 2-D plotter 17 a inFIG. 13 ) that carries the mechanical marking device 24 a. Theelectro-mechanical 2-D plotter 17 a is mounted to a base 14 a of moduleframe 14. The base 14 a has an opening which is configured to allow themechanical marking device 24 a to access and mark the area under theopening. The attachment point 41 is connected to or integrally formedwith a top 14 d of module frame 14. The module frame 14 further includesa multiplicity of vertical support members that connect the base 14 a tothe top 14 d. Only two vertical support members 14 b and 14 c arevisible in FIG. 12A. For example, the frame may have four verticalsupport members, the third and fourth vertical support members beingdisposed behind vertical support members 14 b and 14 c respectively inthe view presented in FIG. 12A.

The module frame 14 further includes a plurality of (at least three)standoff support members 18. A respective surface attachment device 27is coupled to the distal end of each standoff support member 18. In theexample marking scenario depicted in FIG. 12A, the surface attachmentdevices 27 attach or adhere to a surface 9. The surface attachmentdevices 27 may be selected from the following types: magnetic-baseddevices (e.g., an electro-permanent magnet) for ferromagneticstructures, and/or vacuum-based, electrostatic-based, adhesive-based,and gripper-based devices for non-ferromagnetic structure. The standoffsupport members 18 and surface attachment devices 27 form a standoffsystem that maintains the mechanical marking device 24 a at a specifiedrelative position suitable for marking the surface 9.

FIG. 12B is a diagram representing a side view of a marking module 25including an optical marking device 24 b in accordance with anotherembodiment, which marking module 25 may be a payload carried by a UAV 2of the type depicted in FIG. 3A or a type having a different design. Inone proposed implementation, the optical marking device 24 b includes alaser (not shown in FIG. 12B, but see laser 330 in FIG. 23 ) capable ofproducing a laser beam 13 having an intensity sufficient to melt orvaporize the material of the surface to be marked. The module frame 14of the marking module 25 depicted in FIG. 12B may be identical to themodule frame 14 depicted in FIG. 12A. Likewise the module frame 14supports an electro-mechanical 2-D plotter (not shown in FIG. 12B, butsee electro-mechanical 2-D plotter 17 a in FIG. 13 ) that holds theoptical marking device 24 b.

In the marking scenario depicted in FIG. 12B, the marking module islocated so that the optical marking device 24 b is directed to thesurface 9 to be marked. In accordance with one proposed implementation,the optical marking device 24 b is a laser that emits a laser beam 13which propagates parallel to the Z-axis and then impinges on the surface9 to form a laser spot. The laser is configured to produce a light beam13 of sufficient intensity to melt or vaporize the material of thesurface 9 at the laser spot. The laser may be controlled to emitrespective pulses intermittently at different positions as the laserspot is moved by the 2-D plotter (not shown in FIG. 12B) along apredetermined scan path.

In accordance with some embodiments, the marking device is moved over atwo-dimensional (2-D) area by means of an electro-mechanical 2-Dplotter. FIG. 13 is a diagram showing a top view of anelectro-mechanical 2-D plotter 17 a overlying a dent or gouge or othertype of anomaly 1 where material has been removed from the surface 9.The plotter 17 a includes a device holder 28 that holds a marking device24, such as the marking device shown in either FIG. 12A or FIG. 12B. Inaccordance with one proposed implementation, the electro-mechanical 2-Dplotter 17 a includes a device holder 28 that holds a marking device 24(such as the mechanical marking device 24 a shown in FIG. 12A or theoptical marking device 24 b shown in FIG. 12B) for marking a target areaon surface 9. The electro-mechanical 2-D plotter 17 a is movably coupledto the base 14 a of the module frame 14. The marking device 24 issupported by the electro-mechanical 2-D plotter 17 a and configured tocreate marks in accordance with a specified (pre-programmed) patternwhen the surface attachment devices 27 are in contact with the surface9. A computer (not shown in FIG. 13 , but see computer 42 in FIG. 16 )is programmed to control the electro-mechanical 2-D plotter 17 a and themarking device 24 so that marks are produced at multiple spots along apredefined motion path.

In accordance with the embodiment depicted in FIG. 13 , theelectro-mechanical 2-D plotter 17 a includes a first traveling bridge 20a that is slidably coupled to the base 14 a of the module frame 14 fortranslation in an X direction and has a longitudinal slot; and a secondtraveling bridge 20 b that is slidably coupled to the base 14 a fortranslation in a Y direction (perpendicular to the X direction) and hasa longitudinal slot 70 b that crosses the longitudinal slot 70 a. Themarking device 24 is supported by the device holder 28 at a crossing ofthe longitudinal slots 70 a and 70 b. The device holder 28 has a firstportion that is coupled to longitudinal slot 70 a in a manner thatenables the marking device 24 to translate in an X direction and asecond portion that is coupled to longitudinal slot 70 b in a mannerthat enables the marking device 24 to translate in a Y direction. Forexample, the device holder 28 may have one annular projection whichslides in respective linear grooves formed in the sides of longitudinalslot 70 a and another annular projection which slides in respectivelinear grooves formed in the sides of longitudinal slot 70 b. Inalternative implementations, various types of bearings may be employed.

The first and second traveling bridges 20 a and 20 b are independentlytranslatable in the X and Y directions respectively. For example, thefirst traveling bridge 20 a may translate in the X direction while thesecond traveling bridge 20 b does not move relative to base 14 a, inwhich case the marking device 24 is moved in the X direction whilesliding in longitudinal slot 70 b in the second traveling bridge 20 b.Conversely, the second traveling bridge 20 b may translate in the Ydirection while the first traveling bridge 20 a does not move relativeto base 14 a, in which case the marking device 24 is moved in the Ydirection while sliding in longitudinal slot 70 a in the first travelingbridge 20 a. Such movements may be included in a planned motion path.

Still referring to FIG. 13 , the first traveling bridge 20 a hasrespective bearing guides (not shown in FIG. 13 ) at opposite endsthereof, which bearing guides travel (e.g., slide or roll) alongrespective guide rails 68 a and 68 c disposed on opposing sides of base14 a. The first traveling bridge 20 a further includes a motor (notshown in FIG. 13 ) that is operatively coupled to a first pinion gear 66a. The first pinion gear 66 a has teeth which engage teeth of a firstrack 64 a that is disposed parallel to and spaced apart from the guiderail 68 a. The motor may be activated to drive rotation of the firstpinion gear 66 a, which in turn causes the first traveling bridge 20 ato translate in the X direction on guide rails 68 a and 68 c. Similarly,the second traveling bridge 20 b has respective bearing guides (notshown in FIG. 13 ) at opposite ends thereof, which bearing guides travel(e.g., slide or roll) along respective guide rails 68 b and 68 ddisposed on the other opposing sides of the base 14 a. The secondtraveling bridge 20 b further includes a motor (not shown in FIG. 13 )that is operatively coupled to a second pinion gear 66 b. The secondpinion gear 66 b has teeth which engage teeth of a second rack 64 b thatis disposed parallel to and spaced apart from the guide rail 68 b. Themotor may be activated to drive rotation of the second pinion gear 66 b,which in turn causes the second traveling bridge 20 b to translate inthe Y direction on guide rails 68 b and 68 d.

Other linear drive means may be substituted for the rack and pinionarrangement shown in FIG. 13 , such as a lead screw threadably coupledto a nut incorporated in a bearing guide or carriage. In the lattercase, the drive motors would be mounted to the base 14 a of the moduleframe 14 rather than mounted to the bridges as is the case in theexample wherein the drive mechanism is a pinion gear.

Instead of bearing guides sliding or rolling on guide rails, the firstand second traveling bridges 20 a and 20 b may be translatably coupledto the base 14 a of module frame 14 by means of linear motion guides. Inthis implementation, each guide comprises a respective pair of slidablycoupled linear motion guide halves. One pair of linear motion guidestranslatably couples the first traveling bridge 20 a to two opposingsides of base 14 a; another pair of linear motion guides translatablycouples the second traveling bridge 20 b to the other two opposing sidesof base 14 a. As used herein, the term “linear motion guide half” meansa structure having a straight surface that guides a contacting surfaceof another linear motion guide half to move linearly during relativemotion of the two halves. More specifically, the term “linear motionguide half” includes, but is not limited to, male and female slidehalves well known in the art.

FIG. 14 is a diagram showing a top view of an electro-mechanical 2-Dplotter 17 b in accordance with an alternative embodiment. The plotterincludes a carriage that carries a marking device and is translatablealong a traveling bridge having an axis, which traveling bridge in turnis translatable along another axis which is perpendicular to the bridgeaxis. The electro-mechanical 2-D plotter 17 b comprises a travelingbridge 20 c that includes a guide rail 60 and a carriage 62 that isslidably coupled to the guide rail 60. The carriage 62, which carries amarking device (not visible in FIG. 14 ), is translatable along theguide rail 60 in a Y direction. The traveling bridge 20 c istranslatable in an X direction. More specifically, the opposing ends ofthe guide rail 60 are supported by respective bearing guides 72 a and 72b. The bearing guides 72 a and 72 b respectively travel along a pair ofmutually parallel guide rails 68 a and 68 b during movement in the Xdirection. The guide rails 68 a and 68 b are disposed on opposing sidesof the base 14 a of the module frame 14. The electro-mechanical 2-Dplotter 17 b further includes an X motion drive motor 22 a (not shown inFIG. 14 , but see FIG. 14A) that is operatively coupled to driverotation of a pinion gear 66. The pinion gear 66 has teeth which engageteeth of a rack 64 that is disposed parallel to and spaced apart fromthe guide rail 68 a. The X motion drive motor 22 a may be activated todrive rotation of the pinion gear 66, which in turn causes the guiderail 60 to translate in the X direction on guide rails 68 a and 68 b.

The traveling bridge 20 c and carriage 62 are independently translatablein the X and Y directions respectively. For example, the travelingbridge 20 c may translate in the X direction while the carriage 62 doesnot move relative to guide rail 60, in which case the marking device 24(not shown in FIG. 14 , see FIG. 14A) is moved in the X direction.Conversely, the carriage 62 may translate relative to guide rail 60while the traveling bridge 20 c does not move relative to base 14 a, inwhich case the marking device 24 (not shown in FIG. 14 ) is moved in theY direction. Such movements may be included in a planned motion path.

FIG. 14A is a diagram showing a side view of portions of theelectro-mechanical 2-D plotter depicted in FIG. 14 . The travelingbridge 20 c includes bearing guides 72 a and 72 b which respectivelytravel (e.g., slide or roll) along the guide rails 68 a and 68 b (seeFIG. 14 ). The traveling bridge 20 c further includes the X motion drivemotor 22 a that is operatively coupled (via an output shaft) to thepinion gear 66. The pinion gear 66 has teeth which engage teeth of therack 64 seen in FIG. 14 . Opposed ends of the guide rail 60 are fixedlycoupled to the bearing guides 72 a and 72 b. The traveling bridge 20 cfurther includes a bearing guide 72 c which is slidably coupled to theguide rail 60 and a carriage 62 which is fixedly coupled to the bearingguide 72 c. An optical marking device 24 b is fixedly coupled to thecarriage 62, having a dependent configuration to enable marking of asurface area underlying the opening in base 14 a (see FIG. 14 ).

A drive mechanism operatively couples the carriage 62 to a Y motiondrive motor 22 b. The drive mechanism includes a lead screw 76 (threadsnot shown) and a nut (within carriage 62) that threadably engages thelead screw 76. The nut is installed inside a cavity formed in thecarriage 62. The coupling of carriage 62 to the lead screw 76 by meansof the nut enables the bearing guide 72 c to translate (by sliding)along the guide rail 60 when the lead screw 76 is driven to rotate by Ymotion drive motor 22 b. The opposing ends of lead screw 76 aresupported by respective bearings (not shown in FIG. 14A). Rotation oflead screw 76 may be driven by Y motion drive motor 22 b via a belt (notshown) which circulates on respective pulleys. In other embodiments, thelead screw could be driven directly by the motor. Other options includegear drive, cable drive, or chain drive. In accordance with a proposedimplementation, the bearing guide 72 c comprises a series ofrecirculating ball bearings, the balls of which roll along the guiderail 60. Optionally, the position of the carriage 62 along the guiderail 60 can be measured by a position sensor (e.g., a rotation encodercoupled to the lead screw 76) to provide position feedback to the motorcontroller (not shown in FIG. 14A) that controls carriage translation inthe Y direction. Similarly, the position of the traveling bridge 20 calong the guide rail 68 a (see FIG. 14 ) can be measured by a positionsensor to provide position feedback to the motor controller thatcontrols traveling bridge translation in the X direction. In accordancewith an alternative embodiment, a mechanical marking device (e.g., apen) may be substituted for the optical marking device 24 b indicated inFIG. 14A.

Optionally, the marking tool 11 depicted in FIG. 12A is movable betweena retracted (stowed) position and an extended (deployed) position. FIG.is a diagram representing a side view of a mechanical marking device 24a in a state wherein the marking tool 11 (e.g., a pen) is retracted. Inthe retracted state, a contact tip 23 of the marking tool 11 does notcontact the surface 9; in the extended state (not shown in FIG. 15 ),the contact tip 23 contacts the surface 9. The mechanical marking device24 a further comprises a pen-lifting actuator 102 (e.g., a rotationalservo motor) which is mounted to the plotter. The marking tool 11 isconnected to an output shaft (not visible in FIG. 15 ) of actuator 102by means of a hub 104, an arm 106, and marking tool holder 28. The hub104 is attached to an end of the output shaft of actuator 102. The arm106 has a proximal end attached to hub 104. The distal end of arm 106may be a yoke that supports the marking tool holder 28. Thus, themarking tool 11 is rotated when the output shaft of pen-lifting actuator102 rotates.

In accordance with alternative embodiments, the mechanical markingdevice 24 a can be actuated by linear motion instead of rotation. Forexample, the mechanical marking device 24 a can be coupled to theplotter by means of a vertical lifting mechanism. This vertical liftingmechanism may use a rotational servo actuator with a rack-and-pinionmechanism to turn the rotational motion of the servo into linear(translational) motion of the marking tool 11.

FIG. 16 is a block diagram identifying some components of a system fordrawing lines on a surface by moving a marking device 24 a over an areaof a surface using the traveling bridge 20 c partly depicted in FIG. 14. The system depicted in FIG. 16 includes a computer 42 that isprogrammed to collect encoded data representing the spatial coordinatesof the pen-lifting actuator 102 and then process that position data todetermine how to command the plotter and the pen-lifting actuator 102 toensure that a contact tip of the marking device 24 a is positioned at aspecified marking site. The Y position of the pen-lifting actuator 102is tracked using a Y motion incremental encoder 92; the X position ofthe pen-lifting actuator 102 is tracked using an X motion incrementalencoder 90. The pen moves from a retracted position to an extendedposition or vice versa when the pen-lifting actuator 102 is activated.In accordance with some embodiments, the X and Y motion incrementalencoders 90 and 92 may be either optical or magnetic linear encoders.

Upon initiation of a marking task, the computer 42 issues commands whichcause the pen-lifting actuator 102 to be moved to a starting X-Ycoordinate position. Then the computer 42 issues a control signal whichactivates the actuator 102 to rotate the pen into contact with thesurface. Thereafter, the computer 42 issues commands to the plottermotors (not shown in FIG. 16 ) which cause the pen to move along amotion path. The computer 42 receives electrical signals from the X andY motion incremental encoders 90 and 92, which cause the pen to draw acontinuous line or successive connected line segments on the surface ofthe limited-access structure or object. When a line or line segment isfinished, computer 42 issues a control signal which activates thepen-lifting actuator 102 to rotate the pen out of contact with thesurface. Then the routine is repeated for drawing the next line or linesegment. The end result of the marking process proposed herein may analignment grid with alphanumeric symbology, one example of which isdescribed below with reference to FIG. 24 . The computer 42 is alsoconfigured to construct a task completion message to be transmitted to aground control station by a transceiver 38.

FIG. 17 is a block diagram identifying some components of a markingmodule 25 which has an electro-mechanical 2-D plotter and is remotelycontrolled by a control station 40. Electrical power to all electricallypowered components of the marking module 25 is provided by a battery(not shown). As shown in FIG. 17 , the module controller 26 iscommunicatively coupled to all electrical and electro-mechanicalcomponents of the marking module. The module controller 26 includes acomputer 42 and motor controllers 34 which are communicatively coupledto the computer 42. The motor controllers 34 are configured forcontrolling X and Y motion drive motors 22 a and 22 b which drivetranslation of the first and second traveling bridges 20 a and 20 bidentified in FIG. 13 or the first traveling bridge 20 a and carriage 62identified in FIG. 14 . For example, the computer 42 may be programmedto control operation of the X and Y drive motors 22 so that the markingdevice 24 travels along a predefined motion path. In addition, thecomputer 42 controls operation of the marking device 24 and the videocamera 30. The previously described surface attachment devices 27 alsooperate under the control of computer 42.

In the embodiment partly depicted in FIG. 17 , X and Y drive motors 22,marking device 24, and video camera 30 are controlled by the computer 42as a function of radiofrequency commands transmitted by a controlstation 40 on the ground. Those radiofrequency commands are transmittedby a transceiver 44 on the ground, received by a transceiver 38incorporated in the marking module 25, and converted by the transceiver38 into the proper digital format. The resulting digital commands arethen forwarded to the computer 42. The control station 40 may comprise ageneral-purpose computer system configured with programming forcontrolling operation of the marking module 25. In addition, thecomputer system (not shown in FIG. 17 ) of the control station 40 maycomprise a display processor configured with software for controlling adisplay monitor to display images of the surface acquired by the videocamera 30 before, during and, after marking.

FIG. 18 is a block diagram identifying some components of a remotelycontrolled UAV 2 configured to carry a module (not shown). The flight ofthe UAV 2 is controlled by a flight controller 32 as previouslydescribed with reference to FIG. 9 . The UAV 2 includes a video camera31 that provides images for use in flight control. The UAV 2 is alsoequipped with a coupling mechanism (such as coupling mechanism 15depicted in FIG. 10D) which is configured to couple a marking module(not shown in FIG. 18 ) to the UAV 2 and hold the module securely duringflight. The UAV 2 is further equipped with a module release actuator 21that that actuates the coupling mechanism 15 to de-couple from themarking module. The control station 40 may comprise a general-purposecomputer system configured with programming for controlling operationsof both the UAV 2 and the marking module.

FIG. 19 is a block diagram identifying some components of a system forholding (temporarily attaching) a marking module 25 in a stable positionon a surface 9 of a structure using a vacuum adherence system. Thevacuum adherence system includes plurality of suction cups 50, a vacuummanifold assembly 52, an electro-mechanical (e.g., solenoid-actuated)control valve 54 (hereinafter “control valve 54”), and a vacuum pump 56.The vacuum pump 56 is in fluid communication with a first port ofcontrol valve 54; the vacuum manifold assembly 52 is in fluidcommunication with a second port of control valve 54. The plurality ofsuction cups 50 are in fluid communication with the vacuum manifoldassembly 52. The term “manifold” is used herein in the sense of achamber or duct having several outlets through which a fluid can bedistributed or gathered. These manifolds connect channels in the suctioncups 50 to the vacuum system comprising vacuum pump 56 and control valve54. In accordance with alternative embodiments, each individual suctioncup 50 has a respective vacuum motor (not shown in FIG. 19 ).

The computer 42 (previously described with reference to FIG. 9 ) isfurther configured to control the state of control valve 54, whichselectively connects vacuum pump 56 to vacuum manifold assembly 52. Thevacuum manifold assembly 52 comprises a plurality of vacuum manifoldswhich are in fluid communication with respective suction cups 50. Thecomputer 42 may be programmed to send a control signal that causes thecontrol valve 54 to open. In the valve open state, the computer 42 alsosends a control signal to activate the vacuum pump 56. The vacuum pump56 applies a vacuum pressure to the vacuum manifold assembly 52 thatcauses the suction cups 50 to vacuum adhere to the surface being marked.The vacuum pump 56 needs to maintain constant vacuum pressure. Inaccordance with one proposed implementation, the vacuum pump 56 does notoperate continuously; instead the vacuum pump 56 continuously monitorsthe vacuum pressure using a sensor, such as a pressure sensor, under thesuction cups 50 and activates every time the vacuum pressure falls belowa specified threshold. The system will attempt to maintain a pressuredifferential of about 1 to 2 psi below atmospheric pressure.

FIG. 20 is a diagram representing a bottom view of an electro-mechanical2-D plotter 17 c (absent the carriage that carries the marking device)in accordance with an alternative embodiment. As seen in FIG. 20 , theelectro-mechanical 2-D plotter 17 c includes a traveling bridge 300 thatrides on a pair of mutually parallel horizontal linear rails 312 and 314attached to the front face of open frame structure 76. (The linear rail312 is partly hidden behind a lead screw 302 in FIG. 20 .) The travelingbridge 300 is slidably coupled to the horizontal linear rails 312 and314 by means of sliders embedded in respective block connectors 310 and316. The traveling bridge 300 further includes a pair of mutuallyparallel vertical linear rails 320 and 322 disposed perpendicular to thehorizontal linear rails 312 and 314. (The linear rail 320 is partlyhidden behind a lead screw 304 in FIG. 20 .) The vertical linear rails320 and 322 are attached to the block connectors 310 and 316 such thatall four components move in unison. In addition, a carriage (not shownin FIG. 20 ) is slidably coupled to the vertical linear rails 320 and322 by means of sliders 318 (which are shown at middle positions alongvertical linear rails 320, 322 in FIG. 20 ). In accordance with oneproposed implementation, the slider/linear rail assemblies arecaged-ball linear motion guides of a type which are commerciallyavailable from THK Co. Ltd., Tokyo, Japan.

For the purposes of this disclosure, an X-Y-Z coordinate system will beadopted in which the X direction is parallel to the horizontal linearrails 312 and 314, the Y direction is parallel to the vertical linearrails 320 and 322; and the Z direction is perpendicular to the X and Ydirections. The carriage is slidably coupled to the vertical linearrails 320, 322 for translation in the Y direction. The traveling bridge300 is slidably coupled to the horizontal linear rails 312, 314 fortranslation in the X direction.

The electro-mechanical 2-D plotter 17 c depicted in FIG. 20 furthercomprises a pair of lead screws 302 and 304. The lead screw 302 isthreadably coupled to a lead screw nut (not shown in FIG. 20 )incorporated inside block connector 310. The lead screw 304 isthreadably coupled to a lead screw nut (not shown in FIG. 20 ) that isfixedly coupled to the carriage. One end of the lead screw 302 isrotatably seated inside a bearing 308 while the other end is connectedto the output shaft of an X motion drive motor 22 a. Bearing 308 and Xmotion drive motor 22 a are both attached to the base 14 a of the moduleframe. In addition, one end of the lead screw 304 is rotatably seatedinside a bearing 326 while the other end is connected to the outputshaft of a Y-axis motion motor 324. Bearing 326 and Y-axis motion motor324 are both components of the traveling bridge 300. The travelingbridge 300 slides along the horizontal linear rails 312, 314 wheneverlead screw 302 is rotated. The sliders 318 (and carriage attachedthereto) slide along the vertical linear rails 320, 322 whenever leadscrew 304 is rotated. The direction of translation depends on thedirection of lead screw rotation. Thus, a marking device may be movedacross a surface to be marked.

As previously mentioned, the operation of the flying robotic markingplatform may be enhanced by the provision of means for stabilizing themodule frame relative to the structure or object being marked. Thestabilization means employed in the embodiment depicted in FIG. 20include four pneumatic stabilizers 48 a-48 d. Each stabilizer comprisesa contactor 88 which is preferably made of elastomeric material toprovide traction and preclude scratching of the surface of the structureor object when the pneumatic stabilizers 48 a-48 d are in the extendedstate.

FIG. 21 is a diagram identifying some components of a system forstabilizing a distal end of an extended-reach arm using pneumaticstabilizers 48 a-48 d having rod lock mechanisms. As partly shown inFIG. 21 , each pneumatic stabilizer 48 a-48 d is a pneumatic cylinder154 comprising a base cylinder 158, a piston 156 that is slidable insidethe base cylinder 158, and a piston rod 162 connected to the piston 156and extending outside of the base cylinder 158. The contactor 88 isattached to a distal end of the piston rod 162.

The pneumatic cylinder 154 is operatively coupled to a pressureregulator (not shown in FIG. 21 ) which is disposed between a main airsupply 168 and a cylinder valve 172 (e.g., a solenoid valve 164). Thepressure regulator regulates (i.e., reduces) the pressure of thecompressed air supplied by the main air supply 168. The pneumaticcylinders 154 are preferably of the double-acting type, meaning thatthey are capable of moving the piston 156 in either one of oppositedirections to produce either an extend stroke or a retract stroke. Thestate of each cylinder valve 172 is controlled by the computer 42 Thecomputer 42 is configured (programmed) to activate extension of thepiston rods 162 in a stabilization mode by opening the cylinder valves172, thereby causing the contactors 88 to move from their retractedpositions to extended positions whereat the contactors 88 all contactthe surface to be marked.

The pneumatic stabilizers 48 a-48 d are compliant at the start of theprocess in order for all four to make contact the surface with aspecific amount of pressure, and they lock in place to keep the assemblyfrom bouncing around while the marking device is being moved on thesurface. Each pneumatic stabilizer 48 a-48 d further comprises a rodlock (not shown in FIG. 21 ) attached to the base cylinder 158 andconfigured for locking the piston rod 162 to prevent movement. Inaccordance with one proposed implementation, the rod lock 160 preventspiston rod movement upon release of stored energy (i.e., the rod lock160 holds load during power or pressure loss). The rod lock 160 hasdouble-acting locking action for clamping in both directions.

The control computer 42 is configured to cause the pneumatic stabilizers48 a-48 d to extend in unison in response to a stabilize command fromthe system operator or in response to a self-generated stabilize controlsignal when the marking module is properly located on a surface. Thecontrol computer 42 is further configured to cause the rod locks 160 tolock the piston rods 162 in place in response to a lock command from thesystem operator or in response to a self-generated lock control signalwhen the contactors all contact the workpiece surface.

Although the control computer 42 controls the states of all of thepneumatic stabilizers 48 a-48 d, FIG. 21 only shows the components ofone pneumatic stabilizer for the sake of simplicity. The double-actingpneumatic cylinder 158 has two ports to allow compressed air into eitherthe internal volume 164 behind the piston 156 (for the extend stroke ofthe piston rod 162) or the internal volume 166 in front of the piston156 (for the retract stroke of the piston rod 162). Which internalvolume is filled with compressed air from the main air supply 168 isdependent on the state of the cylinder valve 172, which state in turn iscontrolled by control computer 42. The cylinder valve 172 must beenergized during extension and retraction of the piston rod 162. Itshould also be energized at the end of each stroke until a change ofdirection is required. The pneumatic system further comprises a lockvalve 170 that must be energized (to the retracted state) during pistonmotion. When the lock valve 170 is not energized, the rod lock 160 isengaged.

FIG. 22 is a block diagram identifying some components of a compliantstabilizer 48 mounted to base 14 a of marking module 14 in accordancewith an alternative embodiment. In this example, the compliantstabilizer 48 includes an outer tube 82 affixed to base 14 a by means ofa fixed coupling 78, an inner shaft 86 telescoped inside the outer tube82, a contactor 88 mounted to a distal end of the inner shaft 86, and aspring 84 that exerts a spring force that urges the inner shaft 86 toextend until the contactor 88 contacts the surface of the workpiece.This type of spring-loaded stabilizer does not require actuation by acontrol system. It may be useful in some embodiments to have a lockingmechanism.

FIG. 23 is a block diagram identifying components of a control systemthat uses X and Y motion rotational encoders 140 and 142 toincrementally track the relative location (e.g., relative to an initiallocation acquired using a location measurement system, such as a localpositioning system) of a marking device during motion of the markingdevice over the surface. In this example, the marking device is a laser330 carried by a carriage 62, which carriage 62 in turn is slidablycoupled to a traveling bridge 300 of the type depicted in FIG. 20 . Thecontrol system comprises a module controller 26 programmed with motioncontrol application software 144 and marking application software 146.The module controller 26 is communicatively coupled to an X motion drivemotor 22 a (which drives translation of the traveling bridge 300 alongthe horizontal linear rails 312, 314 seen in FIG. 20 ) and a Y motiondrive motor 22 b (which drives translation of carriage 62 along thevertical linear rails 320, 322 of traveling bridge 300). In accordancewith one proposed implementation, the X and Y motion drive motors 22 aand 22 b are stepper motors that do not require feedback from externalencoders for motion control. The module controller 26 is programmed withmotion control application software 144 comprising respective softwaremodules for controlling the motors. The motion control application 144controls the operation of X and Y motion drive motors 22 a and 22 bbased on rotation feedback from respective rotational encoders, namely,X-axis rotational encoder 140 and Y-axis rotational encoder 142. Therotational counts from the encoders are converted into linearmeasurements.

The module controller 26 is connected to the motors and encoders via anelectronics box (not shown in FIG. 23 ). The electronics box containsthe system power supplies and integrates all the plotter controlconnections and provides an interface between the module controller 26and respective flexible electrical cables that connect to the motors.The encoded data from the X and Y motion rotational encoder 140 and 142is processed by the module controller 26 to determine the X-Y coordinateposition of the laser 330. The module controller 26 hosts markingapplication software 146 which is configured to control the operation oflaser 330 as a function of its X-Y coordinate position in the frame ofreference of the structure or object.

One example of markings including intersecting lines and alphanumericsymbology for use in alignment of parts will now be described in somedetail for the purpose of illustration. However, it should beappreciated that markings may include geometric symbology (e.g., lines,line segments, dots) applied in any suitable pattern with or withoutalphanumeric symbology.

FIG. 24 is a diagram representing a plan view of an anomalous area on asurface 9 having markings arranged to form an alignment pattern 46overlying an anomaly 1 for use in an alignment task preliminary torepairing the anomalous area in accordance with one proposedimplementation. The alignment pattern 46 includes an orthogonal grid 120consisting of a network of uniformly spaced horizontal lines 122 andvertical (perpendicular) lines 124 which intersect to form squaretilings or cells (hereinafter “cells”). In alternative implementations,the network of lines may be configured to form triangular or hexagonalcells. In addition to the orthogonal grid 120, the alignment pattern 46includes numeric symbols (numbers) 126 which identify respective rows ofsquare cells and alphabetic symbols (letters) 128 which identifyrespective columns of square cells.

In general, a numbered grid pattern of the type depicted in FIG. 24would be used as a way to identify specific locations that can bereferenced in the future. For example, if someone examining an image ofan anomalous area on a surface noticed a problem and wanted to refer toa specific grid location (e.g., R6), it would be easy for an on-sitetechnician to locate that cell, possibly to perform a repair task or aninspection task, without having to use an additional measurement device,which might introduce a misinterpretation risk (e.g., the measurementperformed by the technician might be made in a different way than theanalysis intended).

In one example scenario, an analyst/inspector may compare a photographof a repaired area that includes a uniformly spaced grid to anon-destructive inspection (NDI) scan of the area. More specifically,the analyst/inspector may use the overlay grid markings to match to thecoordinates of the NDI scan. An overlay grid is especially useful as alocation reference in situations where the photographic image is takenfrom an angle and may have perspective foreshortening or other opticaldistortions that make it difficult to accurately acquire dimensions.

In accordance with some embodiments, the marking system proposed hereinalso includes an off-board tracking system for vehicle and markingdevice localization, which system may be communicatively coupled to theaforementioned control station 40 on the ground. More specifically, theoff-board tracking system is configured to provide three-dimensional(3-D) localization information for navigation and control of the UAV 2relative to the target object and for accurately locating the markingmodule in the frame of reference of the target object and correlatingthe location data with a 3-D model of the target object. Accuratelocation tracking for UAV-based marking will enable the UAV 2 to move amarking module to the proper location and record the 3-D coordinate dataassociated with that location. This 3-D information is important fordocumenting the marking. Any one of various techniques may be used toprovide the information necessary to record the 3-D location of theactivity. The external localization system may also be used to indicateto the operator the coordinates on the target where marks are needed.

In accordance with one embodiment, the UAV includes an onboard trackingsystem that is able to navigate the UAV in accordance with apreprogrammed flight plan. The preprogrammed flight plan carried by UAVenables the UAV to follow a flight path around a portion of the targetobject. The system further includes an off-board tracking system havingmeans for wireless communication with the UAV. The off-board trackingsystem is configured to send commands to or monitor various operatingperformance parameters of the UAV, such as fuel remaining, battery powerremaining, etc. The off-board tracking system may also be used togenerate commands to alter the flight path of the UAV based on acquiredlocalization data.

In accordance with one embodiment, 3-D localization may be accomplishedby placing optical targets (such a retro-reflective targets) on the UAV2 and then using motion capture feedback control to calculate thelocation of the UAV 2. Closed-loop feedback control using motion capturesystems is disclosed in detail in U.S. Pat. No. 7,643,893, thedisclosure of which is incorporated by reference herein in its entirety.In accordance with one embodiment, the motion capture system isconfigured to measure one or more motion characteristics of the UAV 2during a repair mission. A processor receives the measured motioncharacteristics from the motion capture system and determines a controlsignal based on the measured motion characteristics. A position controlsystem receives the control signal and continuously adjusts at least onemotion characteristic of the UAV 2 in order to maintain or achieve adesired motion state. The UAV 2 may be equipped with optical targets inthe form of passive retro-reflective markers. The motion capture system,the processor, and the position control system comprise a completeclosed-loop feedback control system.

In accordance with an alternative embodiment, location tracking of theUAV 2 may be implemented using a local positioning system (not shown inthe drawings) mounted on or near the target object. The localpositioning system may be controlled from the ground and used to trackthe location of a UAV 2 having three or more known visible featuresthereon. A typical local positioning system comprises: a pan-tiltmechanism; a camera mounted to the pan-tilt mechanism; and a laser rangemeter for projecting a laser beam along an aim direction vector ontoeach visible features. The pan-tilt mechanism comprises a motorized panunit and a tilt unit. The camera comprises a housing to which the laserrange meter is mounted. The camera may comprise a still camera (colorand/or black and white) to obtain still images, a video camera to obtaincolor and/or black and white video, or an infrared camera to obtaininfrared still images or infrared video of the visible features. Thelocal positioning system further comprises a computer system which isconfigured to measure coordinates of the visible features in the localcoordinate system of the target object. In particular, this computersystem is programmed to control motions of the pan-tilt mechanism torotationally adjust the camera to selected angles around the vertical,azimuth (pan) axis and the horizontal, elevation (tilt) axis. Thecomputer system is also programmed to control operation of the cameraand receive image data therefrom for transmission to the control station40. The computer system is further programmed to control operation ofthe laser range meter and receive range data therefrom for transmissionto the control station 40. The local positioning system may furthercomprise a wireless transceiver and an antenna to enable bidirectional,wireless electromagnetic wave communications with a control station. Thelocal positioning system preferably has the capabilities described inU.S. Pat. Nos. 7,859,655, 9,285,296, and 8,447,805 and U.S. PatentApplication Pub. No. 2018/0120196, the disclosures of which areincorporated by reference herein in their entireties. The image dataacquired by the video camera of the local positioning system may undergoimage processing as disclosed in U.S. Pat. No. 8,744,133.

An alternative 3-D localization approach involves placing two or moreUAV-placed visible targets, such as ink marks, adjacent to the repairarea. The marks would be used by the UAV to accurately re-orient itselfto the repair during each successive repair operation. Automated videolocalization equipment would be employed to re-orient the UAV to therepair area using the usable marks.

While methods and apparatus for marking of surfaces of UAV-accessiblestructures and objects have been described with reference to variousembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the teachingsherein. In addition, many modifications may be made to adapt theteachings herein to a particular situation without departing from thescope thereof. Therefore it is intended that the claims not be limitedto the particular embodiments disclosed herein.

As used in the claims, the term “controller” should be construed broadlyto encompass a system having at least one computer or processor, andwhich may have multiple computers or processors that communicate througha network or bus. As used in the preceding sentence, the terms“computer” and “processor” both refer to devices having a processingunit (e.g., a central processing unit) and some form of memory (i.e.,computer-readable medium) for storing a program which is readable by theprocessing unit. For example, the term “controller” includes, but is notlimited to, a small computer on an integrated circuit containing aprocessor core, memory and programmable input/output peripherals.

1-8. (canceled)
 9. An apparatus for marking a target surface of astructure or object, the apparatus comprising: a first frame; aplurality of rotor motors mounted to the first frame and capable ofproducing lift greater than a weight of the apparatus; a plurality ofrotors operatively coupled to respective rotor motors of the pluralityof rotor motors; a first controller programmed to control the rotormotors in a manner that produces lift greater than the weight of theapparatus; an arm rotatably coupled to the first frame and having adistal end; a second frame coupled to the distal end of the arm; amarking device supported by the second frame.
 10. The apparatus asrecited in claim 9, further comprising: a plotter movably coupled to thesecond frame, the marking device being carried by the plotter; and asecond controller programmed to control the plotter so that the markingdevice follows a motion path.
 11. The apparatus as recited in claim 10,wherein the plotter comprises: a first traveling bridge slidably coupledto the second frame for translation in an X direction and having a firstlongitudinal slot; and a second traveling bridge slidably coupled to thesecond frame for translation in a Y direction perpendicular to the Xdirection and having a second longitudinal slot that crosses the firstlongitudinal slot, and wherein the marking device is supported at acrossing of the first and second longitudinal slots.
 12. The apparatusas recited in claim 11, further comprising: a first motor operativelycoupled to drive translation of the first traveling bridge in the Xdirection; and a second motor operatively coupled to drive translationof the second traveling bridge in the Y direction, wherein the secondcontroller is programmed to control operation of the first and secondmotors so that the marking device travels along the motion path.
 13. Theapparatus as recited in claim 10, wherein the plotter comprises: atraveling bridge slidably coupled to the second frame for translation inan X direction and comprising a guide rail that is perpendicular to theX direction; and a carriage slidably coupled to the guide rail fortranslation along the guide rail, wherein the marking device is carriedby the carriage.
 14. The apparatus as recited in claim 13, wherein theplotter comprises: a first motor operatively coupled to drivetranslation of the traveling bridge in the X direction; and a secondmotor operatively coupled to drive translation of the carriage along theguide rail, wherein the second controller is programmed to controloperation of the first and second motors so that the marking devicetravels along the motion path.
 15. The apparatus as recited in claim 9,further comprising a rotating ring mount that rotatably couples the armto the first frame, wherein the arm is a telescoping arm.
 16. Theapparatus as recited in claim 10, wherein the marking device is a laserand the second controller is further configured to control operation ofthe laser.
 17. The apparatus as recited in claim 10, wherein the secondframe is releasably coupled to the first frame, further comprising aplurality of surface attachment devices mounted to the second frame. 18.The apparatus as recited in claim 10, wherein the plotter comprises arotary actuator and an arm coupled to the rotary actuator and having adistal end, wherein the marking device is attached to the distal end ofthe arm.
 19. A method for marking a surface of a structure or objectusing an unmanned aerial vehicle, the method comprising: (a) coupling amarking module to the unmanned aerial vehicle; (b) flying the unmannedaerial vehicle to a location in proximity to the surface while carryingthe marking module; (c) placing the marking module into contact with thesurface; and (d) marking the surface using a marking device of themarking module while the marking module is in contact with the surface.20. The method as recited in claim 19, wherein step (c) comprises movinga contact tip of the marking device along the surface.
 21. The method asrecited in claim 19, wherein step (c) comprises: generating a laser beamthat impinges on the surface; and moving the laser beam across thesurface, wherein the laser beam has sufficient energy to melt orvaporize material of the surface at a point of impingement.
 22. Themethod as recited in claim 19, further comprising: (e) coupling aclean-up module to an unmanned aerial vehicle; (f) flying the unmannedaerial vehicle to a location in proximity to the surface while carryingthe clean-up module; (g) placing the clean-up module into contact withthe surface; and (h) removing the marking from the surface using acleaning element of the clean-up module while the clean-up module is incontact with the surface.
 23. (canceled)
 24. An unmanned aerial vehiclefor marking a target surface of a structure or object, the unmannedaerial vehicle comprising: a body frame; a plurality of rotor motorsmounted to the body frame and capable of producing lift greater than aweight of the unmanned aerial vehicle; a plurality of rotors operativelycoupled to respective rotor motors of the plurality of rotor motors; acontroller programmed to control the rotor motors in a manner thatproduces lift greater than the weight of the unmanned aerial vehicle; aninner ring mounted to the body frame; an outer ring that is rotatablycoupled to the inner ring; a telescoping arm comprising an outerproximal tube affixed to the outer ring and an inner distal tube that issupported by and displaceable relative to the outer proximal tube; asecond frame pivotably coupled to the inner distal tube; first andsecond compliant stabilizers supported by the second frame; and a firstmarking device supported by the second frame.
 25. The unmanned aerialvehicle as recited in claim 24, further comprising a counterweight whichis mounted to the outer ring at an angular position which isdiametrically opposed to the telescoping arm.
 26. The unmanned aerialvehicle as recited in claim 25, wherein the outer ring, the telescopingarm, and the counterweight are designed to provide a balanced rotationalsystem that allows the telescoping arm to rotate about the center of theinner ring without changing the location of the center-of-mass of theunmanned aerial vehicle.
 27. The unmanned aerial vehicle as recited inclaim 25, wherein the counterweight comprises: a platform which isattached to or integrally formed with and extending outward from theouter ring; an arm pitch control motor mounted to the platform, whereinthe arm pitch control motor, when activated, drives rotation of theouter ring relative to the inner ring; and an electric power systemmounted to the platform, wherein the electric power system comprises abattery and associated electronics for providing electric power to thearm pitch control motor.
 28. The unmanned aerial vehicle as recited inclaim 24, further comprising third and fourth compliant stabilizerssupported by the second frame, wherein the first marking device and thefirst through fourth compliant stabilizers are arranged so that thefirst through fourth compliant stabilizers contact the target surfacebefore the first marking device contacts the target surface as thesecond frame approaches the target surface.
 29. The unmanned aerialvehicle as recited in claim 28, further comprising second, third, andfourth marking devices, wherein the first through fourth marking devicesand first through fourth compliant stabilizers are arranged so that thefirst through fourth compliant stabilizers contact the target surfacebefore the first through fourth marking devices contact the targetsurface as the second frame approaches the target surface.